Key Facts

UTIs are among the most common bacterial infections. Most uncomplicated lower UTIs in women can be managed empirically without urine culture. Appropriate antibiotic stewardship is essential.

Epidemiology

• Lifetime incidence in women: ~50%; recurrence in 25-30%
• UTI in men: uncommon before age 50; usually indicates underlying pathology
• Incidence increases with age, catheterisation, and institutionalisation
• Most common cause of Gram-negative bacteraemia

Aetiology

• E. coli: 70-80% (community), 50% (hospital)
• Other Gram-negatives: Klebsiella (8%), Proteus (5% – alkaline urine, staghorn calculi)
• Staphylococcus saprophyticus: second most common in young women
• Enterococcus: associated with catheterisation
• Pseudomonas: catheterised/hospitalised patients

Pathophysiology

• Ascending infection from perineum via urethra to bladder (cystitis) and potentially to kidneys (pyelonephritis)
• Short female urethra explains female predominance
• Bacterial virulence factors: P-fimbriae (pyelonephritis), type 1 fimbriae (cystitis)
• Risk factors: female sex, sexual activity, pregnancy, menopause (atrophic vaginitis), catheterisation, urinary obstruction, vesicoureteric reflux, diabetes

Lower UTI (Cystitis)

• Dysuria: burning/stinging on urination
• Frequency and urgency
• Suprapubic pain/discomfort
• Cloudy, malodorous urine
• Haematuria (30% of cases)
• No systemic features

Upper UTI (Pyelonephritis)

• Fever (>38°C), rigors
• Loin/flank pain (unilateral)
• Nausea, vomiting
• Costovertebral angle tenderness
• Symptoms of lower UTI may or may not be present

In Elderly

• May present atypically: confusion, falls, functional decline, incontinence
• Do not treat asymptomatic bacteriuria in the elderly

Red Flags

• Sepsis (high NEWS2 score, tachycardia, hypotension) → IV antibiotics
• Pyelonephritis not responding to oral antibiotics within 48 hours → consider abscess/obstruction
• Recurrent UTI in men → urological investigation
• Haematuria after UTI treated → urological referral to exclude malignancy

Bedside

• Urine dipstick: nitrites (specific) + leucocytes (sensitive); both positive = high PPV
• NEWS2 score: assess for sepsis

Bloods (if systemic features/pyelonephritis)

• FBC, CRP: raised WCC and CRP
• U&Es: renal function
• Blood cultures: if systemically unwell
• Lactate: if sepsis suspected

Microbiology

• MSU for culture and sensitivity: indicated for complicated UTI, treatment failure, recurrent UTI, pregnancy, males, catheterised
• Significant bacteriuria: ≥10⁵ CFU/mL (symptomatic: ≥10³ may be significant)

Imaging

• Not routine for uncomplicated UTI
• Renal USS: if pyelonephritis not responding to treatment (exclude abscess/obstruction)
• CT KUB: if renal stones suspected
• DMSA scan: scarring assessment in children with recurrent UTI

Uncomplicated Lower UTI in Women (NICE NG109)

• First-line: nitrofurantoin 100mg MR BD for 3 days (if eGFR >45)
• Second-line: trimethoprim 200mg BD for 3 days (check local resistance – E. coli resistance ~30% in some areas)
• Third-line: pivmecillinam 400mg stat then 200mg TDS for 3 days
• Empirical treatment without MSU is appropriate in typical presentations

Lower UTI in Men

• Trimethoprim 200mg BD or nitrofurantoin 100mg MR BD for 7 days
• Always send MSU
• Consider prostatitis (14-28 day course of trimethoprim or ciprofloxacin)

Pyelonephritis

• Mild (oral): cefalexin 500mg TDS for 7-10 days or co-amoxiclav 500/125mg TDS
• Severe (IV): IV co-amoxiclav 1.2g TDS or IV piperacillin-tazobactam 4.5g TDS (per local protocol)
• Switch to oral when clinically improving for 24-48 hours

UTI in Pregnancy

• Always treat (including asymptomatic bacteriuria)
• Nitrofurantoin (avoid at term – neonatal haemolysis) or cefalexin 500mg BD for 7 days
• Trimethoprim: avoid first trimester (folate antagonist)
• Send MSU for culture

Recurrent UTIs (≥3/year or ≥2 in 6 months)

• Behavioural measures: adequate hydration, post-coital voiding, avoid constipation
• Vaginal oestrogen cream (postmenopausal women): effective in reducing recurrence
• Antibiotic prophylaxis: nitrofurantoin 50-100mg nocte or trimethoprim 100mg nocte for 6 months
• Post-coital prophylaxis: single-dose antibiotic after intercourse
• Self-start therapy: patient-initiated course at symptom onset
• D-mannose, cranberry products: limited evidence

Referral Criteria

• Recurrent UTI in men → urology
• Recurrent UTI in women → further investigation (USS, cystoscopy if haematuria)
• UTI not responding to treatment → imaging for complications

• Uncomplicated cystitis: >95% cure rate with appropriate antibiotics
• Pyelonephritis: full recovery expected with prompt treatment; 10-20% develop bacteraemia
• Untreated pyelonephritis in pregnancy: 20-40% develop sepsis
• Recurrent UTIs: 25-30% of women experience recurrence within 6 months
• Catheter-associated UTIs: most common healthcare-associated infection; increases morbidity and length of stay

NICE NG109 Antibiotic Choice Summary

Common UTI Organisms